Integrating analog-to-digital converter

ABSTRACT

An integrating analog-to-digital converter comprising: an analog input signal source, first and second analog reference signal sources, integrating means common to the analog input signal source and the first and second analog reference signal sources, a first analog reference signal from the first analog reference signal source having such a polarity as to increase the integrated output from the integrating means in a positive direction in accordance with the supply of the first analog reference signal to the integrating means and the second analog reference signal from the second analog reference signal source being opposite in polarity to the first analog reference signal, a clock pulse source, a pulse counter, means for supplying the integrating means with an analog input signal from the analog input signal source in a predetermined analog input signal integrating time period determined by a clock pulse from the clock pulse source, means for supplying the integrating means with the second analog reference signal or the first analog reference signal according as the integrated output is positive or negative at the time of completion of the integration of the analog input signal by the integrating means in a first one of n&#39;&#39;s reference signal integrating time periods sequentially following the analog input signal integrating time period and determined by the clock pulse, (n being an integer more than 2 and the jth analog reference signal integrating time period being l/2(j-l) times the first one and j 2, 3, . . . n), means for supplying the integrating means with the second analog reference signal or the first analog reference signal according as the integrated output at the time of termination of the (j-l)th analog reference signal integrating time period is positive or negative, and means for supplying the pulse counter with the clock pulse from the clock pulse source in the jth analog reference signal integrating time period when the integrated output from the integrating means at the time of completion of integration of the analog input signal is positive (or negative) and when the integrated output from the integrating means is positive (or negative) at the time of termination of the (j-l)th analog reference signal integrating time period.

1451 Oct. 15, 1974 INTEGRATING ANALOG-TO-DIGITAL CONVERTER [76] Inventor: Tetsutaro Eto, 16-14,

Kamisoshigaya-3, Tokyo, Japan 22 Filed: May9, 1972 21 Appl. No.1 251,678

[30] I Foreign Application Priority Data UNITED STATES PATENTS source having such a polarity as to increase the integrated output from the integrating means in a positive direction in accordance with the supply of the first analog reference signal to the integrating means and the second analog reference signal from the second analog reference signal source being opposite in polarity to the first analog reference signal, a clock pulse source, a pulse counter, means for supplying the integrating means with an analog input signal from the analog input signal source in a predetermined analog input May 11, 1971 Japan 46-31371 Signal integrating time Period determined y a Clock Y pulse from the clock pulse source, means for supply- 52 US. (:1 340/347 NT, 340/347 AD, 235/183 ing the integrating means with the second analog [51] Int. Cl. H03k 13/20 Hence Signal the first analog reference Signal [58] Field of Search 340/347 AD, 347 NT; cording as the integrated Output is Positive or negative 235/133; 324 990 at the time of completion of the integration of the analog input signal by the integrating means in a first one '[56] R f r Cit d of ns reference signal integrating time periods sequentially following the analog input signal integrating time period and determined by the clock pulse, (n being an 3,267,458 8/1966 Anderson et al. 340/347 NT integer more than 2 and the jth analog reference 3,368,149 2/1968 Wasserman.... 340/347 NT db l h r 3,480,948 11/1969 Lord 340/347 NT nteglaungtme Perm emg (l-I) "l 3,500,109 3/1970 Sugiyama et al. 340/347 NT oneimdl means Supplymg the 3,525,093 8/1970 Marshall 340/347 NT a g means with the Second analog reference Signal 3,541,320 11/1970 Beall..; 340/347 NT or the first analog reference signal according as the 3,564,538 2/1971 Bondzeit et al. 3401347 NT integrated output at the time of termination of the 3,566,397 2/1971 Walton..' 340/347 NT (j-l)th analog reference signal integrating time period 3,566,458 2/1971 Reid I 340/347 NT is positive or negative and means for the 3,735,394 5/1973 Eto-. 340/347 NT Primary Examiner-Charles D. Miller Attorney, Agent, or Firm-Marshall & Yeasting pulse counter with the clock pulse from the clock pulse source in the jth analog reference signal integrating time period when the integrated output from the integrating means at the time of completion of integration of the analog input signal is positive (or negative) and when the integrated output from the integrating means is positive (or negative) at the time of termination of the (il)th analog reference signal integrating time period.

6 Claims, Drawing Figures 1 integration ccl.

I 1 ChOngG-MTF a switch amplifier inputsignul 12 source 5 Q jewel 10M VN 1352 R1 P4 d 11mm; P2 n signal i Sli generator 6 1p 0p R3 cl chuggea over ;w|ich 2 source Qupmg d -y 41b pulse ccl. L7 2 P1 13 39C counter :1 R3 p3 R2 36 35 inverlier 3 43 Cpi 38b indicator 36b and gale PAIENIEBIEI 5814 3 8424.1 6

SW55! 1 BF 7 73 int ration cc t. 1 I chunge-over m Swiich amplifier c1 Signal "2' E )I Source 4| 2- 4 I +V b 1 a ll 5 Q .reference C comparator sou; reset switch 32 R1 P4 q 1 19 2 4 1 O 1 timing #1 R4 l 9:22:10! Cl t g Over 7SwItCh Source shaping m 41 b P lse cct. 17 23 39 counter R3, and 43 I P3 Inverter gate r CP 1' 38b indicator I 6 and gate PAIENIEDUBUSW SHEH 30! 7 I 'llHllllllllll HImm i mFlazm IHFIGZNZ I i I I mi SNEETSN? Illlll I I l W III.

l mlllhll I ii ii PATENIED BET i 5 i974 SHEEI 70? 7.

voiicige so r integration cct. l

. I 7 57a 57b 57 57 I pgy g 6 p fi l E 12 OP input signal switc M X source C A P8 Q r p D Z 9 5 Qw reference k C comporabr slgnqli Source 9, p reset switch 0 level it detecting cct. I M chqnge-over k v L 1()[ switch L d- 8 1? 1%; A g 22 H5 14 PO 1 5P1 i timing I 1 9 chcnge-over swltch 53%;: m 3 source shaping pulse cct. 5 17 23 counter indicator f P3 54 Ill Cpl counter and gate Q I I r-' --5|(1 -51b 51 51d coincidence detecting cct.

a fin) Fc Pd 53 1 -53b -53c d getting pz HQ HC s y i e Y e A 6 L I -flip-flop r 2 r r; r

56o K 56b K 56 K 56d K 511 $5) $63k 2 cinci gate 10 60a b 60b 1060c 60d INTEGRATING ANALOG-TO-DIGITAL CONVERTER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an integrating analog-todigital converter adapted such that valve of an analog input signal integrated for a predetermined period of time is converted into a digital valve.

2. Description of the Prior Art In conventional types of analog-to-digital converters an analog input signal is integrated and a digital output corresponding to the level of the analog input signal is produced based on the integrated output. However, the conventional converters are constructed on the assumption that no change occurs in the level and/or polarity of the analog input signal in the integration thereof. Accordingly, these prior converters cannot be used in the case where some changes are expected to occur in the level and/or polarity of the analog input signal during its integration.

SUMMARY OF THE INVENTION One object of this invention is to provide an analogto-digital converter which is adapted to obtain a digital output in accordance with a valve of the analog input signal integrated for a predetermined period of time. The analog-to-digital converter of this invention can be used irrespective of a change in the level and/or polar" ity of the analog input signal during its integration. In the analog-to-digital converter of this invention a digital output is provided in accordance with the level of the analog input signal when no change occurs in the leveland/or polarity of the analog input signal during its integration.

Another object of this invention is to provide a analog-to-digital converter which is designed to produce a digital output of a valve proportional to a valve of an analog input signal integrated for a predetermined period of time.

Another object of this invention is to provide an analog-to-digital converter which is adapted to produce a digital output of a valve corresponding to a valve of an analog input signal integrated for a predetermined period of time best corrected in accordance with the integrated valve.

Still another object of this invention is to provide an analog-to-digital converter which is adapted to produce a digital output of a valve of an analog input signal integrated for a predetermined period of time such that the relation between the integrated value of the analog input signal and the digital output is obtained with a broken line characteristic.

Other objects, features and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an example of an integrating analog-to-digital converter according to this invention;

FIGS. 2A to 2Ud8 are a series of signal waveform diagrams, for explaining the examples of FIGS. 1 and 4;

FIG. 3 is a graph showing the relationship of the number of pulses counted to an analog input voltage; and

FIG. 4 is a block diagram illustrating a modified form of the integrating analog-to-digital converter according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates one example of this invention. In the figure, reference numeral 1 indicates an analog input signal source, from which an analog input voltage V, is supplied to an input terminal 4 of an integration circuit 3 through a fixed contact a and a movable contact c of a change-over switch 2. The integration circuit 3 includes an amplifier 5, an integrating resistor 6 and an integrating capacitor 7 and the amplifier 5 is connected at input side to the input terminal 4 through the integrating resistor 6 and at output side to the input side thereof through the integrating capacitor 7 constituting the so-called Miller integrator construction. An output terminal 8 of the integration circuit 3 is connected to the output side of the amplifier 5 and a reset switch 9 is connected between the input and output sides of the amplifier 5.

Reference numerals 10F and l0N designate first and second analog reference signal sources, respectively. A positive reference voltage +V of a constant level is supplied from the one signal source 10P to the input terminal 4 of the integration circuit through fixed and movable contacts a and c of a change-over switch 11 and a fixed contact b and the movable contact c of the change-over swtich 2. While, a negative reference voltage -V- of a constant level is supplied from the other signal source l0N to the input terminal 4 of the integration circuit 3 through a fixed contact b and the movable contact c of the change-over switch 11 and the fixed and movable contacts b and c of the changeover switch 2. In this case, the voltages +V and V are selected to bear a relationship l+V l-V-ltherebetween.

An integrated output E derived from the output terminal 8 is fed to a comparator circuit 12 which utilizes zero voltage as the reference and is adapted to provide a compared output Q of binary indication which provides an indication 1 when the integrated output E is positive or zero and 0" when the output E is negative. The compared output Q is fed to terminals d of D- type flip-flop circuits l3 and 14.

Reference numeral 15 indicates a clock pulse source from which a clock pulse train CPO of a period 71 such as shown in FIG. 2A is supplied to a waveform shaping circuit 16 to derive therefrom a clock pulse CPl such as depeicted in FIG. 2B which is produced at the time corresponding to the leading edge of each pulse of the pulse train CPO. The clock pulse CPI thus obtained is applied to an input terminal 18 of a timing signal generator circuit 17, which has output terminals 19, 20, 21, 22, 23 and 24. Let it be assumed that the pulses of the pulse train CPI are sequentially produced at times t 2,, t The timing signal generator circuit 17 is adapted to derive a rectangular wave R1 for timing use such as shown in FIG. 2C from the output terminal 19, a pulse train P1 such as shown in FIG. 2D from the output terminal 20, a rectangular wave R2 such as shown in FIG. 2E from the output terminal 21, a pulse P2 such as shown in FIG. 2F from the output terminal 22, a reset pulse P3 such as shown in FIG. 20 from the output terminal 23, and a reset pulse P4'such as shown in FIG. 2H from the output terminal 24. The rectangular wave R1 for timing use is such as depicted in FIG. 2C which has a value l of the binary indication for periods of time represented by 321- T between the times t and between t and between andi and a valve for the other remaining period and has a period T represented by 64-1- 2T The pulse train P1 is such as depicted in FIG. 2D which consists of pulses produced at the times r r r 1 r,,,, t t r t and having the period T respectively. The rectangular wave R for timing use is such as depicted in FIG. 2E which as a value l of the binary indication for periods from L to't r to t and a valve 0 for the other remaining periods of time and has the period T The pulse P2 is such as depicted in FIG. 2F which is produced at the times 15, r and has the period T The reset pulse P3 is such as depicted in FIG. 2G which is produced at the times t 1 respectively, and has the period T The reset pulse P4 is such as depicted in FIG. 2H which has the value 1" of the binary indication for periods of time from to r r to r Q and the value 0 for the other remaining periods of time and has the period T If a first period between first and second pulses of the pulsetrain P1 is taken as the reference T the time of second, third, fourth and fifth periods T ,,T T;, and T between the second and third pulses, between the third and fourth pulses, between the fourth and fifth pulses and between the fifth and sixth pulses of the pulse train P1 bear relationships such as T T,/2 T,/2, T T,/4 T,/2 T T,/8 T /2 and T T 16 T /2, respectively. I

The change-over switch 2 is designed to be controlled by the rectangular wave R1 from the output-terminal 19 of the timing signal generator circuit 17 in such a manner that the movable contact 0 may lie on the fixed contacts a and b'when the rectangular wave R1 has the values 1 and 0 respectively. Further, the reset switch 9 of the aforementioned integration circuit 3 is adapted to be closed by the reset pulse P4 derived from the output terminal 24 of the switching signal generator circuit 17. Moreover, the pulse train P1 and the pulse P2 are applied as trigger pulse trains to trigger pulse input terminals e of the aforesaid flipflop circuits l3 and 14 from the output terminals 20 and 22 of the timing signal generator circuit 17, respectively. In this case, when the pulse of the pulse train P1 is applied to the terminal e of the flip-flop circuit 13 which the compared output 0 fed to its terminal d from the comparator circuit 12 has the value l, the flipflop circuit 13 is set and when the pulse of the pulse train P1 is applied to the terminal 2 while the compared output Q fed to the terminal d has the value 0 the flip-flop circuit 13 is reset. The flip-flop circuit 13 derives from its yes output terminal y a rectangular wave output R3 which has a value l of binary indication while the circuit isset and has a value 0 while the circuit 13 is reset. The change-over switch 11 above mentioned is adapted to be controlled by the output R3 such that the movable contact c of the switch 11 may lie on its fixed contacts a and b when the output R3 has the values l, and 0 respectively. When the pulse P2 is fed to the terminal e of the flip-flop circuit 14 while the compared output 0 applied to its terminal d plied to the terminal e while the compared output 0 fed to the terminal d has the value 0, the flip-flop circuit 14 is reset. The flip-flop circuit 14 derives from its not output terminal n a rectangular wave output R4 which has a value 0 of binary indication while the circuit is set and has a value I while it is reset.

The rectangular wave R2 derived at the output terminal 21 of the timing signal generator circuit 17 is applied to one input line-36a of an and gate circuit having two inputs, while the clock pulse train CPl derived from the waveform shaping circuit 16 is applied to the other input line 36b of the and gate circuit 35. While the rectangular wave R2 has the value l one portion of the clock pulse train CPl passes through the gate circuit 35 to provide a clock pulse train CPl' such as shown in FIG. 21, which is supplied to one input line 38b of an and gate circuit 37 having two inputs. While, the output R3 derived at the yes output terminal y of the aforesaid flip-flop circuit 13 is applied to the other input line 38a of the -and gate circuit 37 through fixed and movable contacts a and c of a change-over switch 39.

One portion ofthe output R3 at the output terminal y of the flip-flop circuit l3 is fed to an inverter circuit 41 to derive therefrom an output R3 which is opposite in polarity to the output R3 (in the case of the output R3 being 1', the output R3 is 0 and, in the case of the former being 0, the latter 1). The output R3 thus obtained is fed to the input line 38a of the and gate circuit 37 through the fixed and movable contacts b and c of the change-over switch 39. In this case, the change-over switch 39 is designed to be switchingly controlled so that its movable contact 0 may lie on the fixed contacts a and [2 while the output R4 derived from the not output terminal n of the flip-flop circuit'14 has the values 0 and 1, respectively.

In the period during which the output R3 and R3 fed to the input line 38a of the and gate circuit 37, has the value 1, the gate circuit 37 permits the passage therethrough of the clock pulse train CPl' fed thereto from the and gate circuit 35 to provide a clock pulse train CPl", which is supplied to a pulse counter 42. In this case, the pulse counter 42 is constructed so that the content of counting is reset by the reset pulse P3 derived from the output terminal 23 of the timing signal generator circuit 17. The pulse counter 42 sequentially counts pulses of the pulse train CPI and the counted content is supplied to an indicator 43, thereby providing a digital indication of the content of counting tent of the counter 42 with when the output R4 is O and a digital indication with when the output R4 is l.

The foregoing has outlined the construction of one I example of this invention and the following will describe its operation on the assumption that the analog input voltage V, from the analog input signal source 1 is negative and that the operation starts from he time to.

Since the rectangular wave R1 derived from the output terminal 19 of the timing signal generator circuit 17 is of the value l between t and t as shown in FIG.

, 2C, the contact 0 of thechange-over switch 2 lies on the side of the contact a in this period. Accordingly, the

input voltage V, is integrated by the integrator circuit where R is the value of the resistor 6 and C that of the capacitor 7.

Thus, the rectangular wave R1 becomes 0 at the time so that the contact c of the change-over switch 2 is changed over to the side of the contact b at the time While, the output Q from the comparator circuit 12 at the time I has the value l because the input voltage to the comparator circuit 12 at that time is the output voltage E from the integrator circuit 3 and becuase the voltage E is positive, and the output Q is applied to the terminal d of the flip-flop circuit 13. At the time t the pulse of the pulse train P1 is derived at the output terminal of the timing signal generator circuit 17 as depicted in FIG. 2D and is fed to the input terminal e of the flip-flop circuit 13. Consequently, the flip-flop circuit 13 is set at the time i and the output R3 derived from the output terminal y becomes 1" at the time so that the contact c of the change-over switch 11 is changed over to the side of the contact a.

Thus, the positive reference voltage +V from the reference voltage source l0P is applied to the integrator 3 through the'contacts a and c of the change-over switch 11 and those b and c of the change-over switch 2 from thetimet and the reference voltage +Vp is thereby integrated. The output voltage E (hereinafter referred to as E derives at the output terminal 8 of the integration circuit 3 at the time I, has a value given by the following equation.

In this case, the value of the voltage +V,. is preselected such that the value |-E,,-| expressed by the following equation v may be less than a predetermined maximum value of the output I+E given by the Equation (1).

The'compared output Q, which is l or 0" at the time i dependent upon whether the value of the output E, at the time t, given by the Equation (2) is positive or zero or negative, is applied to the input terminal d of the flip-flop circuit 13. While, the. pulse of the pulse train P1 derived at the output terminal20 of the timing signalgenerator circuit 17 at the time t shown in FIG. 2D, is applied to the input terminal e of the flipflop circuit 13. Theefore, in the case where the com pared Q is 1" at the time I that is, where the value of the output E,,, is positive'or zero at that time, the flipflop circuit 13 having been held in its set state is not altered to the reset state but in the case where the compared output Q is 0," that is, where the value of the output E is negative,'the flip-flop circuit 13 held in the set state is altered to the reset state. Accordingly, in the event-that the value of the output E is positive or zero.

' at the time I the contact 0 of the changeover switch 11 held on the side of the contact a still remains as it is but, in the event of the output E being negative. the contact 0 of the switch 11 is changed over to the side of the contact b at the time t Where the value of the output E, is positive at the time 148, the reference +V,- is continuously integrated by the integrator 3 from the time I and the output voltage E (hereinafter referred to as E5") derived at the output terminal 8 of the integration circuit 3 at the time r5" has a value given by the following Equation (4a) and where the output E is zero the first term of the Equation (4a) is 0, so that the output E has a value given by the following Equation (4a).

Isis

V dr

Lia

Similarly, if the value of the output E at the time r is positive or zero, the flip-flop circuit 13 is still held in its set state and, if negative, the flip-flop circuit 13 is altered to its reset state. After all, where the value of the output E is positive or zero at the time an output E derived at the output terminal 8 of the integration circuit 3 at the time 1 has a value given by the follow-. ing Equation (5a) or (50) and, if negative, the output E has a value given by the following Equation (5b).

Likewise, in the case where the .value of the output E is positive or zero at the time I an output E derived at the output terminal 8 of the integration circuit 3 at the time t has a value given by the following Equation (6a) or (6a) and, if negative, the output E has a value given by the following Equation (6b).

nto

- by the following Equation (7b).

Thus, at the time 2 the reset pulse P4 which has the value 1 from the time to I is derived at the out- I put terminal 24 of th timing signal generator circuit 17, so that the reset switch 9 is closed from the time to t and the value of the output E derived at the output terminal 8 of the integration circuit 3 from a time a little past to I Consequently, the outputE (hereinafter referred to as E at, the time I is 0.

The times 04 I 96 112 120; H24 121; 127 and 128; 128 mm I116 nut ll-l8 uau 191 and 1923 a correspond to thosi? '32 Us s, 6th 62' as and 64 respectively, at which the same operations as those above described are achieved.

By the way, the rectangular wave R2, which has the value 1 from the time I to I from r to r as depicted in FIG. 2E, is applied to the input line 36a of the and gate circuit 35 to derive therefrom apulse train CPl such as shown in FIG. 21 from the time to I from r to r which is fed to the input line 38b of the and gate circuit 37. While, the rectangular wave R3 derived at the output terminal y ofthe flipflop-circuit 13 has the value I while the circuit 13 is in the set state and has the value 0' while the circuit 13 is in the reset state. Such a rectangular wave R3 is supplied to the input line 38a of the and gate circuit '37 .'Since the compared output Q has the value 1"at I the time as above described, the flip-flop circuit 14 is set by the pulse P2 at the time 1 and accordingly the output R4 derived at its output terminal n always has the value 0" after the time 2 thereby holding the movable contact c of the change-over switch 39 on the side of the contact a.

Accordingly, in the periods during which the rectangular wave R3 has the value l between the times r and I between r and r the pulsetrain CPI- is applied to the and gate circuit 37 to provide a pulse train CPI", which is supplied to the counter 42. In this case, the counter 42 is set in advance at the times t r prior to t e Consequently, the counter 42 counts the number of pulses of the pulse train CPI" derived from the and gate circuit 37 between the times and between t, and m and the number of the pulses counted is indicated in the digital form on the indicator 43 from the times t r until the counter 42 is reset by the pulses P3 obtained at the times r 1, tively. The number of the pulses counted by the counter 42 is obtained as a value proportional to the integrated output I+E Further, in this case, since the output R4 is fed to the indicator 43, the indicator 43 also provides the indication This will become apparent fromthe following concrete example.

Namely, let it be assumed for the-sake .of brevity that the input voltage V, is a constant voltage and that the integrated output |E expressed by the Equation (3). is equal to a maximum value of the output |+E;, |-ex'- pressed by the Equation (1).

In such a case, from the Equations (l) and (3) the following relationship can be obtained:

i i I m d it 7 V 7 1:12 V d V t i 1 act, i-i- RCM i tlgtf lfl P| Therefore, the output E from the integration circuit 3 linearly increases in a positive direction with a gradient corresponding to the values of R and C from the time t and reaches a point X at which the output +E (hereinafter referred to as +E based on the. Equation (I) at the time is produced, as indicated by a line U1 in FIG. 2]. Since the output +E is positive in this case, the compared output Q has the value l I as shown in FIG. 2 K,. Consequently,, the flip-flop cir cuit 13 is set based on the pulse of the pulse train P1 at the time r and the rectangular wave R3 derived at the output .terminal y of the flip-flop circuit 13 comes to have the value l from the time as shown in FIG. 2L,, so that the reference voltage +V,l becomes integrated by the integration circuit 3 from the time If this integration proceeds to the time 1 the time inter-' val between the times t and r and that (T, T T

+ T T T (T being the time between I and t. and bearing a relationship T T between and h are equal to each other. Aaordinglyrthe integrated output E linearly decreases from the position of the r'especoutput E,,,., is positive and the compared output Q has the value 1, so that the flip-flop circuit 13 is held in the set state. Accordingly, the change-over switch 11 is not changed over and the integrated-output E continues to decrease similarly along a straight line joining the point X1 with that X1 from the time I, as indicated by a line U1 and reaches a point Xlat the time at which the output (hereinafter referred to as E,,,,.,

' based on the the Equation (4a) is produced. Also in this case, the output E is positive, so that the integrated output E similarly continues to decrease from the position of the point X1 at the time t,,,, down to a point X1 at the time at which the output E (hereinafter referred to E based on the Equation (5a) is produced, as indicated by a line U1 Thereafter, the integrated output E likewise decreases from the time r down to a point X1, at the time 1 at which the output E (hereinafter referred to as E based on the Equation (6a) is obtained, as indicated by a line U1, Then, the integrated output E still continues to decrease down to a point Xl at the time 1 at which the output E (hereinafter referred to as E based on the Equation (7a) is obtained, as indicated by a line U1 Thereafter, the reset switch 9 of the integration circuit 3 is closed between the time and t,,,, so that the output I E from the integration circuit 3 has the value 0" until the time i a little past r as shown by a line U1 In this case, the outputR3 from the flip-flop circuit 13 has the value 1 for the entire period during which wave R2 has the value l," that is, for the period between the time and [,g, which is half as long as that between the times I and 1 as shown in FIG. 2M, and the pulse CPI" is applied to the counter 42. Thus, the

counter 42 counts 16 pulses in the period from the time 1 to I and, based on the content counted, the indicator 43 indicates that the input voltage V, is, for example, l6V" until the counter 42 is subsequently reset. Thereafter, the counter 42 similarly counts 16 pulses in the periods between the times I and 2, between 1, and 1, and the indicator 43 indicates that the input voltage V, is l6V The indication -16V by the indicator 43 implies that the input voltage V, is negative 16V and is a maximum value of the input voltage V,. r

Assuming that the input voltage |V,| is half as low as that in the foregoing example, that is, the following relationship exists:

creases with a gradient half as small as that of the aforementioned line Ul, and reaches a point X2 at the time at which the output +E,, (hereinafter referred to as i if 65 [the output E from the integration circuit 3 linearly in- +E based on the Equation (1) is obtained, as indicated by a line U2 in FIG. 2J. In this case, the output +E,, is positive, so that the compared output Q has the value 1 as shown in FIG. 2K Consequently, the flip-flop circuit 13 is set based on the pulse of the pulse train P1 at the time r and the rectangular wave R3 de rived at the output terminal y of the flip-flop circuit 13 comes to have the value 1 from the time i as shown in FIG. 2L so that the reference voltage +V, becomes integrated by the integration circuit 3 from the time I If this integration continues until the time the reference voltage +V is the same as that in the case of the aforementioned line joining the points X1,, and XI,,, with the result that the integrated output E decreases from the position of the point X2,, at the time I with the same gradient asthat of the line U1, and reaches a point X2 at the time 1 at which the output E is negative and equal to the output I+E I. Accordingly, the integrated output E decreases from the time 1 along a straight line joining the points X2 and X2,, and reaches apoint X2, at the time I, at which the output E (hereinafter referred to as E,,,. )based on the Equation (2) is produced, as indicated by a line U2,. The point X2, hereinmentioned is a point at which the output E has the value 0" because the time between 1 and t and that between I, and t,,, are equal to each other. Therefore, the output Q has the value l at the time I so that the flip-flop circuit 13 remains in the set state and accordingly the change-over switch 11 is not changed over. The integrated output E continues to decrease from the time t, down to a point X2 at the time at which the output E (hereinafter referred to as E based on the Equation (4a') is obtained, as indicated by a line U2 Since the output E,-,,,,, is negative in this case, the flip-flop circuit 13 is reset by the pulse of the pulse train Pl at the time to provide the output R3 having the value 0. Accordingly, the contact c of the change-over switch 11 is changed over to the side of the contact b, causing the integration circuit 3 to integrate the negative reference voltage -V from the time t,-,,,. As a result of this, the integrated output E increases in a positive direction from the point X2 of the time L as indicated by a line U2 Since |+V, V in this case, the line U2 extends from the position of the point X2 with a gradient reverse to that of the aforesaid line U1 toward the point X2 (the same point as that X1 at which the integrated output E has the value 0"at the time I, and reaches a point X2 at the time r at which the output E (hereinafter referred to as E,,,,. )based on the Equation (5b) is obtained. in this case, the output E is negative and the compared output Q has the value O," so that the flipflop circuit 13 remains in the reset state, and consequently the change-over switch 11 is not changed over. Accordingly, the integrated output E continues to increase in the positive direction from the position of the point X2 at the time r and reaches a point X2, at the time r at which the output E (hereinafter referred to E based on the Equation (6b) is obtained. Also in this case, the output E is positive, so that the integrated output E similarly continues to increase in the positive direction from the position of the point X2, at the time 1,, as shown by a line U2 and reaches a point X2 at the time 1 at which the output E (hereinafter referred to as E based on the Equation (7b) is ob tained. Thereafter, the reset switch 9 is closed between the times r and t,,,, with the result that the output E from the integration circuit 3 is zero from a time a little past i to the time I as shown by a line U2,,. In this case, the output R3 from the flip-flop circuit 13 has the value after the time i as illustrated in FIG. 2L While, the output R4 from the flip-flop circuit 14 has the value 0 after thetime in the same manner as that previously described, as depicted in FIG. 2N Consequently, the pulse train CPI is derived from the and gate circuit 37 only between the times t,,, and L as shown in FIG. 2M, and is applied to the counter 42. In this case, the time between i and t,-,,, is half as long as that between 1,, and 1, so that the counter 42 CQUIItjflgllLBillSGS andthe indicator 43 indicates it. In

Y this case, the indicator provides a n indication t hat tEe input voltage V, is -8V because +16V is indicated in the casewhere the counter 42 counts 16 pulses as previously described. Thereafter, the counter 42 similarly counts eight pulses in the periods between t, and r,,,,, between r and A respectively and the indicator 43 thus indicates that the input voltage V, is -8V. The present example has been described on the assumption that the value of the input voltage V, is

half as much as that in the above case in which I6V is indicated, that is, the relationship expressed by the Equation (9) is adopted. Accordingly, the indication of 8V" implies that the input voltage V, is accurately indicated.

Further, if the input voltage V, is zero, the output E from the integration circuit 3 is zero between the times 1,, and I as indicated by U3 in FIG. 2]. However, the.

compared output Q has he value f l at the time 2,, as depicted in FIG. 2K so that the output R3 from the flip-flop circuit 13 comes to have the value I from the time r,,,. As a result of this, the reference voltage +V, is integrated by the integration circuit 3 from the time and accordingly if this integration is carried out until the time t,,,, the integrated output E decreases with the same gradient as that ofthe line U2, from the position of the point X3 of the output E being zero at the time 1 as in the above case and reaches a point X3 at the time t,,, at which the output E has a value equal to the negative output l+E,, Accordingly, the integrated output E decreases from the time along a line joining the points X3, and X3,,' (increases in the negative direction) as indicated by a line U3, and reaches a point X3, at the time 2 at which the output E (hereinafter referred to as E,,,.,,) based on the Equation (2) (the first term being zero) is obtained. In this case, the value of the output E, is negative and equal to that of the aforesaid output |+E so that the compared output Q has the value 0 at the time t,,, and the flip-flop circuit 13 is reset at the time t,,, and the output R3 therefrom has the value 0. Therefore, the change-over switch 11 is changed over to cause the integration circuit 3 to integrate the reference voltage V As-a result of this, the integrated output E increases from the point X3, in'the positive direction to reach av position X3, (the same position as the point X2 at the time at which the output E (hereinafter referred to as E,,,,.,,) based on the Equation (4b) is obtained, as indicated by a line U3 In this case, the output E is negative, so that the output R3 from the flipflop circuit 13 still has the value 0. Accordingly, the integrated output E increases from the point X3 along a line U3 (the same as the line U2 to reach a point X3 (the same as that X2 then still increases from the point X3 along a line U3 (the same as that U2 to a from the point X3, along a line U3 (the same as that i U2,,) to a point X3 (the same as that X2 Thereafter, the reset switch 9 is closed between the times and t,,,, so that the output E from the integration circuit 3 is Zero from a time a little past t,,,, to the time 1 as indicated by a line U3,,. In this case, the output R3 from the flip-flop circuit 13 has the value l only between the times I and I, as shown in FIG. 2K,,. While, even if the output R4 from the flip-flop circuit 14 has the value 0 after the time in the same manner as previously described as illustrated in FIG. 2N the clock pulse train CPI is applied to the and gate circuit 37 only between the times 1,, and t,,,, so that the clock pulse CPI" is not derived from the and gate circuit 37 as depicted in FIG. 2M,,. Consequently, the counter 42 does not count any pulse between the times t and t and the indicator 43 provides an indication that the input voltage V, is O." Thereafter, the counter 42 similarly does not count any pulse between the times t,,, and t,,,,, between r and r so that the indicator 43 provides an indication that the input voltage V, is 0V. Since the input voltage V, is zero in the present example, this implies that an accurate indication of the input voltage V, can be obtained.

A description will be given, though not in detail, in connection with the case where the input voltage V, is a constant negative voltage and is'five-eighths times that in the case where the digital value of l 6V is indicated by the indicator 43, that is, the following relationship is adopted.

I I i I /B'V II (Ill) The integrated output E from the integrator circuit 3 increases in the positive direction from the time t,', to reach a point X4,, at the time r at which the output E has a value five-eighths times that of the aforesaid output E that is, a value /s'E,,- (hereinafter referred to as'E,, as shown by a line U4,,. From the point X4,, the integrated output E decreases down to a point X4, at the time at which a value E,,,., ofa positive output I E,,, (E Eg,,.,)| based upon the Equation (2) is obtained, as indicated by a line U4,. The integrated output E further, decreases from the point X4, and becomes negative and reaches a point X4 at the time t,-,,, at which a value -E of a negative output IE (E E I based on the Equation (4a) is obtained, as indicated by a line U4 and, further, the integrated output E increases from the point X4, in the positive direction to reach a point X4,, at the time t,,,, at which the output E has the value 0" based on the Equation (5b), as shown by a line U4 and from thence the output E increases in the negative direction to a point X4, at the time at which it has a value E,,, equal to a negativeoutput i'iE z 1| based on the Equation (6a), as indicated by a line U4 and from thence the output E further increases in the positive direction to a point X45 at the time r, at which it has a value E equal to a negative output ]+E,, as

a indicated by a lin e U4 and, the integrated output E pulses in all between the times t and t and the indicator 43 indicates that the input voltage V, is 10V." A56 between th e times I64 and rm. between [12,7553 1, the indicator 43 similarly provides the indication of lV." This implies that an accurate indication of the input voltage V, is obtained, because l6 X /s= l0 based on the relationship of the Equation (10). Also in the event that the input voltage V, is negative and has a value other than that in the foregoing, a digital indication is similarly provided corresponding to the value of the input voltage V,. After all, in the above example, an analog-to-digital conversion characteristic expressed by the following function.

l ll

is obtained as shown in FIG. 3 in which the ordinate represents the value of the input voltage |V,| and the abscissa the value of the counting number N of the counter 42.

A brief description will be made in connection with the case where the input voltage V, has a certain positive value and the operation similarly starts from the time I ln the same manner as that previously described the input voltage +V, is integrated by the integration circuit 3 from the time t and at the time the integrated output E is obtained with a value E given by the following equation corresponding to the aforesaid Equation (1).

Further, the contact 0 of the changeover switch 2 is changed over to the side of the contact b from the time 1 While, the compared output 0 has the value 0 at the time 1 because the output E;, is negative, so that the output R3 from the flip-flop circuit 13 does not become 1' but remains O at the time and the change-over switch 11 is not changed over. As a result of this, the integration circuit 3 comes to integrate the negative reference voltage *V from the reference voltage source ION from the time 1 to produce the integrated output E having a value E given by the following equation at the time 1 In this case, the value of the voltage V is selected such that the value of an integrated output IE 'I expressed by the following equation:

as is the case with the Equation (3) may be less than a case-where the input voltage V/is negative, ifthe output E at the time t given by the Equation 13) is positive or zero, the integrated output E is obtained as an output E given by the following Equation (150) or 15a) and if negative. it is obtained as an output E given by the following Equation 15b).

Similarly, if the output E at the time t expressed by the Equation (15a) or (15b) is positive or zero, the integrated output E at the time r is obtained as an output E given by the following equation (16a) or 16a) and if the former is negative or the output E;, expressed by the Equation (l5a'), the latter is obtained as an output E given by the following Equation (16b).

Further, the integrated output E at the time is similarly obtained as an output E given by the following Equation (17a) or (l7a') when the output E at the time t expressed by the Equation (16a) or (1611) is positive or zero and given by the following Equation (17b) when the output E is negative or the output E expressed by the Equation (1611). Likewise, the integrated output E at the time r is obtained as an output E 5 given by the following Equation (18a) or when the output E at the time 1 is positive or zero and given by the following Equation (18b) when the output E is negative, and, further, the integrated output E is made zero from a time a little past the time r to the time 1 1 I62 V d E E I 1.7

62 60 RC the N 1 [63 15 I62 Vpdt (18a) 1 tea E,;;;& M P (1821) 1 163 t 3 62+ N (18b) the times S-h 96, 112, 120 124, H26 127 and 128; I123, 50, I116, t gg, I190, In and [192; COrreSpOnd t those t r r r r r 1 and t respectively as previously described and the same operations as above described are achieved.

Also in this example, the pulse trains CPI and CPI are derived from the and gate circuits 35 and 37, respectively in the same manner as in the case of the input voltage V, being negative and the pulses of the pulse train CPI are counted by the counter 42 and the number of the pulses thereby counted is indicated by the indicator 43 until resetting of the counter 42 in the same manner as in the case of the input voltage V, being negative. The number of pulses counted by the counter 42 is obtained as a value proportional to the integrated output |E given by the Equation (12). Although not described in detail, this will becomes more apparent from the following concrete example.

For the sake of brevity, let it be assumed that the input voltage V, is a certain positive voltage and that the output l+E,,-'| expressed by the Equation (14) is equal to a maximum value of the output |E by the Equation (12). The integrated output E increases in the negative direction from the time t reaches a point X at the time I at which it has a negative value -E equal to lE based on the Equation (12), as shown by a line U5 from thence the output E increases in the positive direction to reach a point X5 at the time at which it has a value E,,,. half times smallerthan that of the output E based on the Equation (13), as indicated by a line US,, from thence the output E increases in the positive direction to reach a point X5 at the time t,,,, at which it has a value E half times smaller than that of the output IE I based on the Equation (15b), as indicated by a line U5 from thence the output E increases in the positive direction to reach a point X5 at the time at which it has a value E half times smaller than that of the output lE based on the Equation (16b), as indicated by a line U5 from thence the output E increases in the positive direction to reach a point X5 at the time r at which it has a value -E half times smaller than that of the output |E,,,,. based on the Equation (17b), as indicated by a line U5 and from thence the output E further increases in the positive direction to reach a point X5 at the time at which it has a value E,,;,. half times smaller than that of the output E,; based on the Equation (18b), as indicated by a line U5 and the output E has the value 0 from a time a little past the time to the time r In this case, the compared output Q, the output R3 from the flip-flop circuit 13, the

1-6 output R3 from the-inverter circuit 41 and the pulse train CPI" from the and gate circuit 37 are obtained as illustrated in FIGS. 2K 2L 20 and 2M respectively.

Consequently, the counter 42 counts sixteen pulses in all between the times t and t and the indicator 43 indicates 16V. Since the output R4 for this indication is always 1, a sign is added to the indication 16V and +16V" is indicated by the indicator 43. Also between the times i and r between r and I the indication +16V" is similarly provided by the indicator 43. In the example, the input voltage V, has a value equal to the absolute value IV ,I of the voltage V, in the case of 16V being indicated by the indicator 43 but is positive in polarity. Accordingly, the indication +16V implies that the voltage Voltage V, is accurately indicated.

Assuming that the input voltage V, is a certain positive voltage and that the output voltage |E expressed by the Equation (12) is five-eighths times that in the above example, the integrated output E increases in the negative direction from the time t and reaches a point X6 at the time 1 at which it has a value E five-eighths times smaller than the aforesaid negative output E,, based on the Equation (12), as indicated by a line U6 from thence the output E increases in the positive direction to reach a point X6, at the time I at which it has a value E,,,.,, of the output {IE J (|E |E based on the Equation (13), as indicated by a line U6 from thence the output E increases in the positive direction to become positive and reach a point X4 at the time 2 at which it has a value +E5|; 4 Of the positive Output E56.5| 'E32 5| |E;, based on the Equation (15b), as indicated by a line U6 from thence the output E increases in the negative direction to reach a point X6 at the time at which it has the value 0 based on the Equation (16a), as indicated by a line U6 from thence the output E increases in the negative direction to reach a point X4, at the time at which it has a value E equal to that of the negative output IE,, .,l based on the Equation (17a'), as indicated by a line U6 and from thence the output E increases in the positive direction to reach a point X6 at the time r at which it has a value |E equal to that of the negative output |E based on the Equation (18b), as indicated by a line U6 and the output E is made zero from a time a little past to the time In this case, the compared output Q, the outputs R3 and R4 from the flip-flop circuits 13 and 14, the output R3 and the pulse train CPl" are obtained as illustrated in FIGS. 2K,;, 2L,, and 2N,,, 20 and 2M,,, respectively.

Accordingly, the pulse counter 42 counts ten pulses in all between the times t and t and the indicator 43 indicates that the input voltage V, is 10V. Further, the indicator 43 indicates that it is and accordingly it provides an indication +10V. Also between the times t and 2, between r and the indication +10V is similarly provided by the indicator 43. In the present example, the voltage |-E is tiveeighths times that in the case where the indication 16V" is obtained, so that +16 X /a=+10 and the indication +10V implies that the input voltage V, is accurately indicated. Also in the case where the input voltage V, is positive and has a value other than that in the foregoing, a digital indication can be likewise obtained corresponding to the value of the input voltage 17 V, and, after all, an analog-to-digital conversion characteristic I shown in FIG. 3 is obtained.

The foregoing has been described to obtain the analog-to-digital characteristic expressed by the Equation l l or shown in FIG. 3. It will be seen from the foregoing that if the values of the reference voltages |+V and |-V, are increased by or times or the time T for integration of the input voltage V, is increased by or times (a being a desired positive number), an analogto-digital conversion characteristic expressed by the Equation (19) can be obtained.

Referring now'to FIG. 4, another example of this invention will hereinbelow be described in detail.

In the present example elements corresponding to those in FIG. 1 are identified by the same reference numerals and characters and no detailed description will be repeated therefor. The present example has the following construction in addition to that of FIG. 1.

Namely, for example, four coincidence detecting circuits 51a to 51d are provided, which are adapted to be supplied with a counted output G from a counter 52 and setting outputs F, to F, representative of digital values from setting circuits 53a to 53d, respectively. In this case, the counter 52 is constructed to count a clock pulse train CPI" produced by supplying the clock pulse train CPl from the waveform shaping circuit 16 to an and gate circuit 54. While, the aforesaid timing signal generator circuit 17 has another terminal 55 in addition to the aforementioned ones, from which is derived a rectangular wave R5 such as depicted in FIG. 2P which has the value l between the times and r between and 1, and has the value in the other periods, and the and gate circuit 54 is adapted to be open in the periods during which the rectangular wave R5 has the value l Accordingly, the pulse train CPI" is obtained between the times and between 1 and 1, as shown in FIG. 20. Further, the setting circuits 53a to 53d are designed so that their setting outputs F to F,, can be set from the outside in the form of different digital values but in the order of F F,,, F, and F.

When the value of the counted ouptut G coincides with the setting outputs F F F and F,,, respectively, coincidence outputs H II H, and H, are sequentially derived from the coincidence detecting circuits 51a, 51b, 51c and 51d, respectively and the coincidence output I-I. is applied to a reset terminal r of a flip-flop circuit 56a and a set terminal s of a flip-flop circuit 56b,

the output H, a reset terminal r of the flip-flop circuit 56b and a set terminal s of a flip-flop circuit 56c, the output H, a reset terminal r of the flip-flop circuit 56c and a set terminal s of a flip-flop circuit 56d and the output H a reset terminal r of the flip-flop circuit 56d. To a set terminal s of the flip-flop circuit 56a is applied the pulse P2 from the output terminal 22 of the timing signal generator circuit 17. Further, each of outputs K to K,, from yes output terminals y of the flip-flop circuits 56a to 56b is supplied to the one input line of each of and gate circuits 57a to 57d having two inputs.

.While, a zero level detecting circuit 58 is provided which is adapted to be supplied with the pulse P2 from the output terminal 22 ofthe timing signal generator circuit 17 andthe compared output Q from the comparator circuit 12 and to obtain a detected output L each time supplied with the pulse P2, which output L has the value l from the time of obtaining the pulse P2 until the compared output Q is altered from l to 0 or 0 to I" and has the value 0" in the other periods. The output L from the zero level detecting circuit 58 is supplied to the other input lines of the aforesaid and gate circuits 57a to 57d.

Further, four voltage sources 59a to 59d are provided corresponding to and gate circuits 57a to 57d and voltages V, to V are applied from these voltage sources 59a to 59d to the input side of the amplifier 5 of the integration circuit 3 through switches 60a to 60d respectively and a common resistor 61. In this case, the switches 60a to 60d are adapted to be closed in the periods during which outputs M, to M from the and gate circuits 57a to 57d have the value 1, respecfrom I to 0" or 0" to l." Accordingly, between the times I and between r and t the outputs M to M from the and" gate circuits 57a to 57d have the value 0," so that the operations between the times t and between t and t are exactly the same as those in the example of FIG. 1. However, since the output L from the zero level detecting circuit 58 has the value l between the times r and 1 between t and r the following operation is obtained in addition to the operations previously described in connection with FIG. 1.

Assume that digital numbers such as, for example, 6, l0", l4 and 17 are set in the setting circuits 53a, 53b, 53c and 53d, respectively. Further, let it be assumed that a resistor 61 has a value R equal to that of the resistor 6, that the voltages V,,, V,, and V derived from the voltage sources 59a, 59b and 590 are negative, that the voltage V,, derived from the voltage source 59d is positive and that the values of the voltages V,, to V,, relative to the voltage V are preselected so that the following relationship may be obtained in relation to the voltage E given by the aforesaid Equation (3).

In such a case, the counter 52 counts pulses of the pulse train CPl from the time and at the time when the counter 52 has counted six pulses of the pulse train CPl' the pulse output H is derived from the coincidence detecting circuit 51a as depicted in FIG. 2R Similarly, at the times r r and t when the counter 52 has counted 10, I4 and 17 pulses of the pulse train CPl" from the time t respectively, the outputs H H and IL, are derived from the coincidence detecting circuits 51b, 51c and 51d as shown in FIGS. 2R 2R and 2R,,, respectively. Accordingly, the outputs K K K and K derived at the tes" output terminals y of the flip-flop circuits 56a, 56b, 56c and 56d are obtained in the form of the outputs 1 between the times and i between i and between and 2 and between t and t as illustrated in FIGS. 28 28 28 and 28 respectively.

Further, since the compared output is 1 at the time as is the case with the foregoing example and is applied to the zero level detecting circuit 58, the output L therefrom is l from the time I by the cooperation with the pulse P2 shown in FIG. 2F. Therefore, the output M,, from the and gate circuit 570 is 1" from the time so that the switch 60a is closed from this time and the voltage V, is applied to the integration circuit 3.

Consequently, if the output L, that is, the compared output 0 continues to have the value I from the time to I only the output M,, has the value l between the times and 1 based on theoutput K depicted in FIG. 28 so that the voltages +V and V,, are integrated by the integration circuit 3 between the times and t Since the integrated output E derived at the output terminal 8 of the integration circuit 3 at the time is given by the following Equation (21) similar to the aforementioned (I), the integrated output E (hereinafter referred to as E obtained at the time 2 has a value given by the following Equation (22).

V-V,, (If RC In 1 If the output L from the zero level detecting circuit 58 has the value l between the times i and t only the output M,, has the value l between the times 1, and based on the output K depicted in FIG. 2S to close only the switch 60 between the times and t during which the voltages +V, and V,, are integrated by the integration circuit 3 and the integrated output E (hereinafter referred to as E therefrom at the time i has ev yg ivsnpy lsfq hw q equation- I50 I (VI-Wadi (23) 1 tea E58 E50 E '50 (VI' V dt 24) Then, if the output L has the value I between the times and only the output M has the value l between the times t and based on the output K, depicted in FIG. 25,,, so that the switch 60d is closed between the times and r In this case, if the integration circuit 3 is not held reset by the reset pulse P4 of FIG. 2H between the times and the voltages +Vp and +V are integrated by the integration circuit 3 between the times and r and the integrated output E (hereinafter referred to as E6 has a value given by the following equation at the time t In this case, however, the voltages V, to V are selected to satisfy the Equations (20a) to (20d) in relation to the voltage V numbers such as 6, l0, l4 and 17 are set in the setting circuits 53a to 53d respectively and the time intervals between the times r and between and t between and and between 2 and t are set to be 101- 81' 81' and 61' respectively, as will become apparent from the follow- Thus, when the compared output Q has the value 0" at the time t,,, the output L has the value 0" after the time t Thereafter, any of the outputs M, to M,, does not become l after the time t and hence any of the switches 59a to 590' is not closed after the time I As a result of this, only the voltage +Vp is integrated by the integration circuit 3 between the times t,, and t and the integrated output E at the time t has a value E given by the following equation.

Further, after the operation has thus been achieved until the time I the output L from the zero level detccting circuit 58 does not become 1" between the times t and t. as previously described, so that any of the outputs M to M,, does not come to have the value -l" between the times t and t and any of the switches 60a to 60d is not closed. Accordingly, the same integration as above described is achieved and the integrated output E at the time t has a value E given by the following Equation (28). If the output E at the time r is positive or zero, the output E obtained at the time has a value given by the following Equation (29a) or (290') and if negative, the output E has a value E given by the following Equation (29b). Further, if the output E at the time r is positive or zero, the output E obtained at the time has a value E given by the following Equation (30a) or (30a) and if negative, the output E has a value E given by the following Equation (30b). Moreover, the output E obtained at the time has a value E expressed by the following Equation (3 la) or (3 la) or (3 lb) according as the output E at the time 1 is positive or zero or negative.

When the output L has thus become 0" at the time t,,, the voltage +V, is integrated between the times t and t in the same manner as that in the foregoing and at the time I the output E is provided to have a value expressed by the following Equation (33).

Vt RC After the operation has thus been carried out until the time I the output E based on the Equation (28), the output E based on the Equation (29a), (2941) or (29b), the output E based on the equation (30a), (30a') or (30b) and the output E based on the Equation (31a), (310') or (31b) are obtained at the times t 2 I and r respectively in the same manner as that above described.

Further, after the integrated output E has been obtained at the time I as above described, if the output L has the value 0 at a time between the times I and 1 the voltage +V, is similarly integrated between the times and t and the output voltage E (hereinafter referred to as E,,') at the time 1,, is provided to have a value given by the following equation which is zero.

When the output L has thus become l at the time the voltage +Vp is-likewise integrated between the times n, and r and the output E is provided to have a value given by the following Equation (35) at the time [56.

After the operation has thus proceeded to the time t the outputs E E and E are obtained at the times 2, I and respectively based on the Equations (29b), (30a), (3011') or (30b) and (31a), (3la) or (31b) in the same manner as that above described.

In the event that the output L comes to have the value 0 at a time t between the times and I56 after the output E at the time r has been obtained based on the Equation (23 the voltages +V and V are integrated between the times and t to provide the in- E 'i' E50 Vpdt Where the output L becomes at a time t, between the times t,-,,,and t after the output E50 at the time I, has been obtained based on the Equation (23) as above described, the voltages +V,and V,. are integrated between the times and t, to provide the output E having a value given by the following Equation (38) at the time t, and then the voltage +V, is integrated between the times t, and t,,,, to provide an output E,,,, given by the following Equation (39) at the time Thereafter, outputs E and E based on the equations (30b) and (31a), (3la') or (311)) are similarly obtained at the times and I respectively.

. l E= E C 50 RC '50 (VP V )d[ 0 (38) 1 60 E60 E t c p (39) Where the output L has the value 0 at a time t,, between the times t and after the output E at the time 1 has been obtained based on the Equation (24) as above described, an output E is obtained at the time I, based on the following Equation (40), an output E at the time 1 based on the following Equation (41 the output E at the time based on the Equation (32b) and the output E,;;, at the time i based on the Equation (3 la), (3 la) or (3 lb). If the output E has the value 0 at the time 1,, between the times r and after the output E,-,,, has been obtained based on the Equation (24) at the time as above described, an

output E based on the following Equation (42), an

. output E based on the following Equation (43) and the output E based on the equation (31b) are obtained at the times r,,, 1 and respectively. If the output L becomes 0" at a time t,," between the times and 1,, after the output E based on the Equation (24) has been obtained from the time 1 outputs E,," and E,,;, given by the following Equations (44) and (45) are obtained at the times 1,," and t,,;,, respectively.

E 1 60 V d 00- RC [(1 1' r as RC ['58 I+V,i)dt0 (42) JET-"F l V d 43 t 62 RC Id P A E:ET 1 1'3 1 '63 ss=fi m Vpdt (45 After the time 1 the times t,,,,,, 1, 1, and 1 r r r and t,,,,,; correspond to I 1 and t, and the same operations as those above described are achieved. I

In the periods during which the output R3 from the flip-flop circuit 13 has the value 0, the pulse train CPI" are derived from the and gate circuit 37 as is the case with the foregoing example and the pulses of the pulse train CPI" are counted by the counter 42 and the number of pulses counted by the counter 42 is indicated by the indicator 43 as is the case with the foregoing example.

Accordingly, the number of pulses counted by the counter 42 is obtained in such a form that the integrated output +E of the Equation (21) has been corrected according to its value. Namely, in the example of FIG. 1, the input voltage V, is constant and the input voltage V, and the counting number N of the counter 42 bear the relationship given by the Equation l I and indicated by I in FIG. 3. In the example of FIG. 4, in the range of N 0 to N (6-1 5 the value of the input voltage V, is obtained with the relationship given by the following Equation (46) and indicated by a line II,, in FIG. 3.

i l IAN In the range of N 5 to N (l0l') 9 the value of the input voltage V, is obtained with the relationship given by the following Equation (47) and indicated by a line H, in FIG. 3.

In the range ofN =9 to N =(l4l)= 13 the value of the input voltage V, is obtained with the relationship given by the following Equation (48) and indicated by a line II, in FIG. 3. I 

1. An analog to digital converter comprising in combination: a. an integrating amplifier means, b. a source of clock pulses, c. a timing signal generator that produces timing pulses that define for each conversion cycle a series of time intervals the first and second of which are selected portions of a conversion cycle and each of the remainder of which is half the preceding interval, d. means for applying a signal of unknown amplitude and polarity to said integrating amplifier only during the first timing interval of each conversion cycle to obtain an amplifier output representative of the unknown signal, e. means for applying signals of known amplitude and polarity to said amplifier during the second and each of the following time intervals to reduce the amplifier output toward zero, and f. means for counting the clock pulses during those time intervals following the second interval and during only those time intervals in which the polarity of the amplifier output at the start of the interval is the same as the polarity of the amplifier output at the end of said first time interval.
 2. An analog to digital converter according to claim 1 in which said timing signal generator is controlled by the clock pulse generator and provides timing signals marking the beginning and end of each of said time intervals and of the conversion cycle.
 3. In an analog to digital converter according to claim 1, a flip-flop circuit, means responsive to the polarity of the amplifier output for conditioning the flip-flop circuit, means for triggering the flip-flop circuit from said timing signal generator, and means responsive to the flip-flop circuit for selecting the polarity of the known amplitude signals for each time interval.
 4. In an analog-to-digital converter according to claim 1, a digital indicator and means for supplying the digital indicator with a counted output from the pulse counting means and in which a digital value is indicated by the digital indicator corresponding to the integrated output at the time of completion of integration of the analog input signal with the integrating means.
 5. In an analog to digital converter according to claim 1, a source of supplementary signals of known amplitude and polarity, means connected to said source for applying the supplementary signals to said amplifier during a time interval starting with the start of the second time interval and terminating upon a reversal of the polarity of the output of the amplifier.
 6. In an analog to digital converter according to claim 1 at least one source supplying a supplementary signal of known amplitude and polarity, presettable counting means connected to indicate selected counts of the series of clock pulses of each conversion cycle, and switch means arranged to connect said supplementary source To the amplifier during a time interval determined at least in part by the accumulation of selected counts in said presettable counting means. 